(CNN) – A United States Secret Service agent traveling with Mitt Romney accidently left a firearm in the lavatory of his charter airplane Wednesday during a trip to Indianapolis.

The firearm was discovered by a reporter for CBS News/National Journal, who told a flight attendant about it, according to a story posted by CBS News. Romney was traveling from Tampa, Florida to Indianapolis, Indiana to deliver a speech.Follow the Ticker on Twitter: @PoliticalTicker, catch the latest updates from the GOP convention on CNN's 2012 Conventions Live Blog, and check out the CNN Electoral Map and Calculator to game out your own strategy for November.

Romney, who will formally accept the Republican presidential nomination Thursday, was seated in the front of the airplane that consisted of campaign aides, reporters and U.S. Secret Service agents.

"We are aware of the incident," Secret Service spokesman Ed Donovan said in a statement. "We take the care and custody of our equipment, especially firearms, very seriously. This matter will be dealt with internally and in an appropriate matter."